Several reasons are causing aircraft manufacturers to try motorizing aircraft wheels, in particular by using drive actuators having electric motors. Such motorization presents significant environmental and economic advantages (reduction in fuel consumption, reduction of noise during taxiing, etc.), and makes it possible to perform new functions: moving the aircraft while its propulsion engines are not operating, taxiing in reverse, remotely controlling the aircraft while it is on the ground, etc.
Designers and systems integrators have studied numerous architectures for actuators for driving aircraft landing gear wheels.
In a first type of architecture, an actuator for driving a wheel in rotation comprises a brushless electric motor, a stepdown gearbox having two reduction stages, a clutch device, and a third stepdown stage driving the wheel in rotation tangentially via connecting rods. In that type of architecture, a relatively large number of parts are permanently connected to the wheel and are subjected to the same mechanical stresses as the wheel (acceleration, vibration, impacts, etc.), thereby raising difficulties of reliability of operation for the drive actuator, and more generally for the function of driving the wheel as performed by the actuator.
In a second type of architecture, the clutch device is replaced by the action of the connecting rods that couple and uncouple the stepdown gearbox and the wheel. That type of architecture is mechanically complex and not very robust. Furthermore, inaccurate positioning of the connecting rods, in particular when coupling at speed when the landing gear and the wheel are deformed, makes it necessary to use coupling rods that are voluminous and thus difficult to integrate between the wheel and the landing gear leg.
In a third type of architecture, the actuator comprises a brushless electric motor, a reduction unit comprising a gearbox and a pinion connected to the outlet of the stepdown gearbox, the pinion meshing with a toothed ring fastened on a rim of the wheel. The actuator is engaged and disengaged relative to the wheel by moving the stepdown unit radially closer to or further away therefrom, thereby enabling the pinion to mesh with the toothed ring or to be separated therefrom. That architecture presents oscillations in the transmission of torque, thereby reducing the lifetime of the drive train.
In order to remedy the above-described drawbacks, proposals have been made to use a drive actuator architecture involving one or more friction rollers associated with means for pressing the friction rollers against the wheel or against a slip track (or ring) mounted on a rim of the wheel in order to cause the wheel to turn. The designs of the drive actuator and of the drive roller itself need to comply with particularly strict requirements applicable to equipment mounted at the bottom of landing gear, where integration of the equipment must be robust in the face of the relatively large amounts of deformation to which wheel rims in particular are subjected, and that equipment must withstand particularly high levels of impact and vibration on landing and while braking after landing.